Try the Russian Baby Maker Stretch
And yes, that tightness will just show up. I am 48 and feel pretty stiff most of the time,even know I am pretty darn flexible for lack of a better word. It really only takes a little time to loosen everything up when I grab the barbell.
Try stretching a bit in the shower. Sounds creepy but I will usually squat and floss around in the bottom position and stretch my hamstrings.
I don't use ROMWOD but seeing ROMWOD Instagram related posts, I have been doing a lot of those moves anyway. Funny thing is, over the years, a lot of the stretches I do, I do because I saw some Russian weightlifter doing it.
I have been considering going to Yoga a couple days a week.